Import polygons with predefined coordinates
Your best bet is to use the Wavefront .obj format. As it's written in ASCII, it's fairly easy to generate.

A simple introduction to the specification of this format is as follows:

#This is a comment

o Object      #Defines an object named Object
              #All the vertices, edges and faces below this belong to this object
              #Until another object is declared

v 1.0 1.0 1.0 #Defines a vertex at the XYZ coordinates 1, 1, 1 
              #and adds it to the list of vertices, like an array (starts at index 1)

f 1 2 3 4     #Creates a face defined by the indexes 1, 2, 3 and for
              #Which refer to the vertices in the list above


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For the complete specification, please see this page.

To import it, you can just go to the 3D View header, press File, then Import, and then Wavefront (.obj). This will bring you to the file browser, where you can choose your file, and in the bottom left corner, choose some extra settings.